1. Field of the Invention
The present invention relates to balloon dilation catheters, and more particularly concerns a catheter having improved pushability, trackability and time of inflation.
2. Description of Relevant Art
Therapeutic balloon dilation catheters, used for balloon angioplasty, are known in the art which are of the so-called "monorail" Configuration. Such monorail catheters generally have a comparatively short distal monorail portion of the catheter slidably received over a guide wire. This distal portion includes an expansible dilation balloon. Other than the comparatively short distal portion of the guide wire received within the catheter, the remainder of the guide wire is exposed externally of the catheter. The monorail portion is coupled with a catheter body tube formed of a flexible material that allows the catheter to be pushed through curved vascular pathways and also enables passage of a balloon inflation fluid. Some typical balloon dilation catheters are shown in U.S. Pat. Nos. 5,217,482 to Keith; 4,762,129 to Bonzel; 5,061,273 to Yock; and 4,748,982 to Horzewski et al.
During angioplasty a guide catheter with a guide wire therein is initially inserted into a patient and serves both to guide a therapeutic catheter along the vascular pathway to a location close to the heart and to protect the patient's blood vessels from trauma which could be caused by contact with the therapeutic catheter.
The guide catheter, with the guide wire in place, is pushed along the vascular pathway until the distal end of the guide catheter reaches a position adjacent but somewhat short of the position at which the angioplasty is to take place. Beyond the distal end of the guide catheter the guide wire is extended through the stenosis of the vascular area that is to be treated. A therapeutic catheter, having the expansible dilation balloon on a distal extremity, is inserted into the guide catheter and over the guide wire, which extends through the monorail section along the guide wire of the therapeutic catheter, so that the catheter is guided beyond the end of the guide catheter to the treatment location. While the balloon is positioned at the treatment location, a dilation fluid is injected into the therapeutic catheter body tube and inflates the thin wall expansible dilation balloon to enlarge the stenosis.
The therapeutic catheter is formed of a body tube that performs a number of functions. It provides the axial drive or push that moves the collapsed and folded balloon at the distal end through the vascular pathways. For this reason certain proximal portions must be relatively stiff and have a high "pushability", although the catheter bends in the vascular pathway. The catheter body tube also forms a lumen that provides a flow path for dilation fluid. In order to decrease inflation and dilation time, the lumen cross-section must be as large as possible and still fit within the guide catheter, which in turn must fit within the vascular pathway. In certain types of angioplasty it is desirable to provide a positive purge of fluid within the dilation balloon to ensure that the latter is free of air before using the therapeutic catheter. To facilitate positive purging, the body tubes of some balloon dilation catheters are formed of a single plastic extrusion having a triad of three side-by-side integral lumens, one to flow fluid distally, a second to flow fluid proximally, and a third to accept an axially insertable stiffening wire to stiffen and strengthen the integral extruded plastic side-by-side tubes. Such an arrangement is expensive and of relatively large diameter, limiting its use to larger vascular pathways. Its pushability is relatively low, requiring a stiffening wire which uses a significant part of the cross-section of the total flow area available. U.S. Pat. No. 5,061,273 to Yock shows a catheter having a multi-lumen body tube.
If the conventional therapeutic catheter body tube is made of a flexible plastic, it loses pushability and may not be able to drive the balloon to its proper position. If made of a stiffer plastic, it may not readily follow the curvature of vascular pathways. If it is stiffened with an integral wire, flow area is lost and inflation and deflation time is increased. Therefore, prior catheters have involved a compromise among several conflicting requirements.
In the monorail type of catheter, both the guide tube that extends through the inflation balloon and the guide wire itself exit the therapeutic catheter body at a guide wire port in the side wall of the body tube. This area of the catheter is weakened by the guide wire port and has a tendency to kink severely as the catheter is moved along the vascular pathway, and as the wire traverses the guide wire port.
Accordingly, it is an object of the present invention to provide a balloon dilation catheter that avoids or minimizes above mentioned problems.